The spring thaw also means millions of defrosting zombies, however, and if the past year has taught her anything, it's that life in this new world is highly imperfect. When Safe Zones throughout the country begin to disappear and the zombies at the fences grow in number, Cassie clings to the hope that if she has the people she loves most, it will be all right. But the highly imperfect world makes only one guarantee - zombies never die, never stop, and are never satiated.